Classes of compounds known as 2-substituted-4-substituted-1,3-oxathiolanes have been found to have potent antiviral activity. In particular, these compounds have been found to act as potent inhibitors of HIV-1 replication in T-lymphocytes over a prolonged period of time with less cytotoxic side effects than compounds known in the art. These compounds have also been found active against 3TC-resistant HIV strains. These compounds are also useful in prophylaxis and treatment of hepatitis B virus infections.
Cis-2-Hydroxymethyl-4-(cytosin-1′-yl)-1,3-oxathiolane can be produced by the methods described by Mansour et al., “Anti-Human Immunodeficiency Virus and Anti-Hepatitis-B Virus Activities and Toxicities of the Enantiomers of 2′-Deoxy-3′-oxa-4′-thiacytidine and Their 5-Fluoro Analogues in vitro”, J. Med. Chem., (1995), Vol. 38, No. 1, pp. 1-4, as well as U.S. Pat. No. 6,228,860 or Nucleosides and Nucleotides, (1995) 14(3-5) pp. 627-735 which are incorporated herein by reference.
Typically, when compounds are desired as a single enantiomer they may be obtained either by resolution of the mixture of the two cis enantiomers by chiral HPLC or by stereospecific synthesis from isometrically pure starting material or any convenient intermediate. A complete review of known technology may be found in “Enantiomers, Racemates and Resolutions” by J. Jacques, A. Collet & S. H. Wilen (John Wiley & Sons, 1981). Alternatively, compounds or any convenient intermediate may be resolved by enzymatic resolution with a suitable enzyme such as cytidine deaminase or selective enzymatic degradation of a suitable derivative. See for example Storer et al., “The resolution and Absolute Stereochemistry of the Enantiomers of cis-1[2(Hydroxymethyl)-1,3-Oxathiolan-5-Yl)Cytosine (BCH-189): Equipotent Anti-HIV Agents”, Nucleosides & Nucleotides, 12(2), 225-236 (1993).
Another process known as resolution by formation of diastereomeric compounds require intervention of chiral agents. Unlike enantiomers, diastereomers may have significantly different physico-chemical properties that may allow for the separation from one another. One variation of such technique involves the formation and separation of diastereomeric salts between a racemic substance and an optically active resolving acid or base. Pasteur first reported the resolution of a racemic acid using an optically active base (Pasteur, L., C. R Acad. Sci. (1853) 37 p. 162; Pasteur, L., Ann. Chim (Paris) (1853) 3, 38 p. 437). A resolution using nonstochiometric quantities of chiral agents was studied by Marckwald 1896 and later referred to as “method of half-quantity” (Marckwald, W., Ber. (1896), 29, p. 42; Marckwald, W., Ber. (1896), 29, p. 43). The process for the resolution of tartaric acid through crystallization of its salt of cinchonine was improved by Marckwald while using only half of the cinchonine necessary for formation of the tartrate salt. The resolution is based on the separation of one of the diastereomers and one of the enantiomers rather than the separation of two diastereomeric salts formed in equal quantities. When using the method of half-quantity, the racemate is partially neutralized by the optically active resolving agent. In the process described by Pope & Peachey (Pope, W. J., Peachey, S. J. J, Chem. Soc. (1899) 75, p. 1066) the excess of racemate not neutralized by the resolving agent is neutralized by the addition of the necessary quantity of an achiral acid or base (depending on whether the resolving agent was an acid or base).